The science of analytical chemistry has, and continues to make progress. The field involves the ability to assay sample materials to determine if a particular substance or substances are present, and if so, the amount of that substance. Frequently, the term “analyte” is used to describe the substance being tested. This term will be used hereafter.
Early examples of the application of analytical chemistry include litmus paper, as well as devices which would change color if atmospheric humidity was above a particular level. To say that the field has become more sophisticated since then is an understatement.
One area of importance in analytical chemistry is the testing and evaluation of liquid samples. While “liquid sample” as used hereafter refers to materials such as blood, urine, but most particularly for this disclosure, water.
It is desirable and necessary to analyze water for various components. For example, it may be important to determine if a water sample is potable. Further, water samples are used for different purposes. Depending upon the use to which the sample is to be put, one or more parameters, such as pH, total alkalinity, calcium hardness, total hardness, and amount of particular analytes such as total chlorine, free chlorine, combined chlorine, sodium content, etc., may be important. For example, when the water sample is taken from a swimming pool, either or both of combined chlorine and free chlorine may be important. Where the water is to be used for an industrial cooling system, total alkalinity or total hardness may be important. When the water is to be used in the health profession, any number of analytes may be of interest and important. These are just examples of the type of uses to which water samples may be put. The skilled artisan will be familiar with many others, which need not be set forth here. Further, the literature on analysis of liquid samples other than water is vast.
Analysis of water samples can be accomplished with any number of different systems. Generally, however, these systems can be divided into “dry chemistry” and “wet chemistry” systems.
In a wet chemistry system, essentially one adds either a liquid testing agent or a dissolvable testing agent to a liquid sample. The testing agent reacts with the analyte of interest, leading to formation of a detectable signal. Preferably, this is the formation of a visible “marker,” such as a color or change in color. Again, the artisan will be familiar with other systems such as measurement of light absorption in photometers, etc. For purposes of this disclosure, however, the discussion will focus on visible formation and changes in color, rather than systems such as light photometers solely to facilitate understanding.
In these wet chemistry systems, the reacted liquid sample is then compared to some reference standard. Generally, this takes the form of a coded reference linking concentration of the analyte to a particular color or degree of color. A low concentration may be indicated by a very pale pink color, and a high concentration by one which is dark red, and vice versa.
Dry chemistry systems can be used to analyze many of the types of samples that wet chemistry systems are used to analyze. In these dry chemistry systems an apparatus, such as an absorbent pad or a test strip is impregnated, coated, or printed with the test system discussed supra, in such a way that the test system does not and cannot leave the apparatus. The apparatus is contacted with the liquid sample, removed from it, and the signal is “read” on the apparatus. As with wet chemistry systems, the signal that is generated is compared to a coded reference to link the signal generated to a specific amount and/or concentration of an analyte under consideration.
The prior art literature on analytical chemistry is vast. For example, U.S. Pat. No. 5,811,254, to Wu, teaches reagent systems which can be used to detect total available chlorine over an extensive range (0 to 5000 ppm). The reagents can be incorporated into a carrier matrix, such as filter paper, to produce a dry chemistry test strip useful in measuring total available chlorine. U.S. Pat. No. 5,710,372, to Becket, teaches test strips which include a plurality of test regions. Each region contains a different amount of a reagent system which reacts with an analyte of interest. A visual display results which permits the user to determine the amount of the analyte in the sample being analyzed. U.S. Pat. No. 5,620,658, to Jaunakais, teaches multicomponent test strips which contain reagents capable of converting undetectable analytes into detectable ones, via ionic change. U.S. Pat. No. 5,529,751, to Gargas, teaches a pH adjustment kit. Once the pH of the sample has been determined, a first reagent is added until the sample indicates that a proper pH has been obtained. The number of drops of the first reagent is then converted to a quantity of a second reagent, which is then used to modify pH of the source of the sample. U.S. Pat. No. 5,491,094, to Ramana, et al., teaches dry reagent test strips for determining free chlorine, using TMB derivatives. U.S. Pat. No. 4,904,605, to O'Brien, et al., teaches test strips which can be used to determine a plurality of different reagents. A dipstick containing a plurality of reagent pads is contacted to sample, signal is formed, and then compared to a reference standard. U.S. Pat. No. 4,481,296, to Halley, teaches compositions that are useful in determining the pH of a halogen containing solution.
As the number of swimming pools and spas increases, the need for effective tools to monitor and control pool water chemistry and especially sanitizer levels becomes more and more important. This is especially true in pools used by the public where the bather concentration is high and the threat of contagious diseases is always present. In order to control the harmful microorganism population of pools, it has been found over the years that chlorine is the most effective and economical sanitizer. However, as popular as chlorine is, it nevertheless has certain drawbacks which must be considered. A particularly serious problem associated with the use of chlorine in outdoor pools is that it tends to be destroyed by sunlight.
In this regard it has been found that the addition of cyanuric acid (2,4,6-trihydroxy-1,3,5-triazine) to pool water can be effective as an extender or stabilizer for chlorine. However, the concentration must be rather carefully adjusted since too little obviously is ineffective as a stabilizer for the chlorine while too much can dramatically slow down the rate at which microorganisms are destroyed by the chlorine. It has been found that the effective concentration of cyanuric acid lies between 30 and 100 parts per million (ppm).
In order to maintain the effectiveness of the cyanuric acid in the swimming pool, it is necessary to measure the concentration thereof using a test device or concentration measuring system. The current test most commonly used in the swimming pool industry involves the melamine turbidimetric method. In this scheme, melamine is added to a sample of the pool water which, in the presence of cyanuric acid, causes the formation of a finely dispersed precipitate. The turbidity created by this precipitate formation is proportional to the amount of cyanuric acid present. By measuring this turbidity using visual or instrumental schemes, an estimation of the concentration of cyanuric acid can be obtained. This test however is not completely acceptable since turbidimetric methods tend, in general, to be unreliable in that other factors can cause turbidity and precipitates are obviously less homogenous than solutions.
For this reason, attempts have been made over the years to replace the turbidimetric analytical procedures with colorimetric methodologies.
Various approaches have been suggested for determining cyanuric acid in samples. For example, U.S. Pat. No. 2,986,452 to Merek suggests the addition of sodium acetate and a soluble copper salt. Mancini, U.S. Pat. No. 4,039,284, utilized a combination of thymolsulfonphthalein and monoethanolamine.
With Stillman, U.S. Pat. No. 4,793,935, more modern systems can be seen. This patent teaches that cyanuric acid, when reacted with melamine, forms a precipitate thus removing the cyanuric acid from water. It is not an analytical method.
U.S. Pat. No. 4,855,239 to Rupe uses melamine as a component of an indicator system for determining cyanuric acid, and Fernando, U.S. Pat. No. 6,432,717, involves an improvement on this earlier patent using a stabilizing compound. Ghanekar, published Application U.S. 2003/0147777, uses an indicator which changes color in response to a change in pH as a way to determine cyanuric acid.
Melamine is somewhat structurally related to the compound acetoguanamine, or 2,4-diamino-6-methyl-1,3,5-triazine, differing in that melamine has an amino group at position 6, whereas acetoguanamine has a methyl group.
While there is this element of structural similarity, it has been found that, among compounds structurally related to melamine, the 6-alkyl derivatives, acetoguanamine, in particular, are useful in cyanuric acid assays, as will be shown in the disclosure which follows.